Multi-zone bipolar ablation probe assembly

ABSTRACT

A medical probe assembly, tissue treatment system, and method are provided for ablating tissue. The probe assembly comprises an elongated member and electrode elements mechanically coupled to the distal end of the elongated member. The electrode elements are configurable as two bipolar electrode pairs with a common electrode element. At least one of the electrode elements comprises a plurality of electrodes (such as, e.g., needle electrodes) radially extendable from the elongated member. An ablation source, such as a radio frequency source, can be connected to the probe assembly in order to convey ablation energy to the electrode pairs, either simultaneously or sequentially.

FIELD OF THE INVENTION

The field of the invention relates generally to the structure and use ofradio frequency (RF) electrosurgical probes for the treatment of tissue,and more particularly, to electrosurgical probes having multipletissue-penetrating electrodes that are deployed in an array to treatlarge volumes of tissue.

BACKGROUND OF THE INVENTION

The delivery of radio frequency (RF) energy to target regions withintissue is known for a variety of purposes of particular interest to thepresent invention. In one particular application, RF energy may bedelivered to diseased regions (e.g., tumors) for the purpose of ablatingpredictable volumes of tissue with minimal patient trauma. RF ablationof tumors is currently performed using one of two core technologies.

The first technology uses a single needle electrode, which when attachedto a RF generator, emits RF energy from the exposed, uninsulated portionof the electrode. This energy translates into ion agitation, which isconverted into heat and induces cellular death via coagulation necrosis.In theory, RF ablation can be used to precisely sculpt the volume ofnecrosis to match the extent of the tumor. By varying the power outputand the type of electrical waveform, it is theoretically possible tocontrol the extent of heating, and thus, the resulting ablation. Thediameter of tissue coagulation from a single electrode, however, islimited by heat dispersion.

The second technology utilizes multiple needle electrodes, which havebeen designed for the treatment and necrosis of tumors in the liver andother solid tissues. U.S. Pat. No. 6,379,353 discloses such a probe. Theablation probe disclosed in U.S. Pat. No. 6,379,353, referred to as theLeVeen Needle Electrode, comprises a cannula having a needle electrodearray, which is reciprocatably mounted within the cannula to alternatelydeploy the electrode array from the cannula and retract electrode arraywithin the cannula. The individual electrodes within the array havespring memory, so that they assume a radially outward, arcuateconfiguration as they are deployed from the cannula. In general, amultiple electrode array creates a larger lesion than that created by asingle needle electrode.

When creating lesions using needle electrode arrays, RF energy iscommonly delivered to the tissue in one of several ways. In the firstarrangement illustrated in FIG. 1, RF current may be delivered to anelectrode array 10 in a monopolar fashion, which means that current willpass from the electrode array 10 to a dispersive electrode 12 attachedexternally to the patient, e.g., using a contact pad placed on thepatient's flank. In a second arrangement illustrated in FIG. 2, the RFcurrent is delivered to an electrode array 20 in a bipolar fashion,which means that current will pass between “positive” and “negative”electrodes 22 within the array 22. Bipolar arrangements, which requirethe RF energy to traverse through a relatively small amount of tissuebetween the tightly spaced electrodes, are more efficient than monopolararrangements, which require the RF energy to traverse through thethickness of the patient's body. As a result, bipolar electrode arraysgenerally create larger and/or more efficient lesions than monopolarelectrode arrays. To provide even larger lesions, it is known to operatetwo electrode arrays in a bipolar arrangement. For example, FIG. 3illustrates two electrode arrays 30 and 32 that are configured to emitRF energy between each other. Specifically, the first electrode array 30is operated as an active electrode array that emits RF energy, and thesecond electrode array 32 is operated as a return electrode array thatreceives the RF energy, thereby ablating the tissue between theelectrode arrays 30 and 32.

Physician feedback has indicated that there is a continuing need fortreating larger tissue volume. For the electrode configurationillustrated in FIG. 3, the distance between the two electrode arraysaffects the volume of tissue ablated. For example, if the distancebetween the electrode arrays were to be lengthened to try to ablate alonger tissue volume, the energy transmitted between the electrodearrays may thin and not fully ablate the intermediate tissue. As aresult, an hour-glass shaped ablation, rather than the desired uniformcircular/elliptical ablation, would be created.

As a consequence, when ablating lesions that are larger than thecapability of the above-mentioned devices, the common practice is tostack ablations (i.e., perform multiple ablations) within a given area.This requires multiple electrode placements and ablations facilitated bythe use of ultrasound imaging to visualize the electrode in relation tothe target tissue. Because of the echogenic cloud created by the ablatedtissue, however, this process often becomes difficult to accuratelyperform. This considerably increases treatment duration and requiressignificant skill for meticulous precision of multiple electrodeplacement.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, a medicalprobe assembly for ablating tissue is provided. The probe assemblycomprises an elongated member, which in the preferred embodiment, isrigid to allow for percutaneous or laparoscopic introduction into apatient's body. The probe assembly further comprises electrode elementsmechanically coupled to the distal end of the elongated member. Theelectrode elements are configurable as two bipolar electrode pairs,wherein the other electrode element is common to the bipolar electrodepairs. In this manner, the electrode elements are configured in a uniquebipolar arrangement that is capable of efficiently ablating tissue. Theelectrode elements can be variously configured to form the bipolarelectrode pairs. For example, two of the electrode elements can beactive elements, and the other electrode element a return element. Or,the two electrode elements can be return elements, and the otherelectrode element an active element. The electrode elements can bestatically configured (i.e., any given electrode element has a dedicatedfunctionality, either an active element or a return element, but notboth) or dynamically configured (i.e., any given electrode element canbe either an active element or a return element during any given time).

In a preferred embodiment, the electrode elements are mounted to theelongated member in an axial arrangement to allow efficient ablation oftissue along its thickness. At least one of the electrode elementscomprises a plurality of electrodes (such as, e.g., needle electrodes)radially extendable from the elongated member. Although the presentinvention should not be so limited in its broadest aspects, the radiallyextendable electrodes allows the probe assembly to generate athree-dimensional lesion (i.e., a lesion that linearly extends along thelength of the elongated member and radially extends from the elongatedmember). Each of the other electrode elements can optionally comprise aplurality of electrodes that radially extend from the elongated memberin order to provide additional three-dimensionality to the lesion.Alternatively, one or more of the electrodes may comprise other types ofelectrode(s), such as ring electrodes. Optionally, additionalelectrode(s), which may also be radially deployable from the elongatedmember, can be mechanically coupled to the distal end of the elongatedmember. In this manner, a longer three-dimensional lesion can becreated.

In accordance with a second aspect of the present invention, anothermedical probe assembly for ablating tissue is provided. The probeassembly comprises an elongated member, which in the preferredembodiment, is rigid to allow for percutaneous or laparoscopicintroduction into a patient's body. The probe assembly further compriseselectrode arrays mechanically coupled to the distal end of the member.Each of the electrode arrays comprises a plurality of needle electrodes.The electrode arrays are configurable as two bipolar electrode pairs,wherein the other electrode array is common to the bipolar electrodepairs. In this manner, the electrode arrays are configured in a uniquebipolar arrangement that is capable of efficiently ablating tissue. Theelectrode arrays can be variously configured to form the bipolarelectrode pairs in the same manner previously described with respect tothe electrode elements. Although the present invention should not be solimited in its broadest aspects, the electrode arrays allow the probeassembly to generate a three-dimensional lesion. In a preferredembodiment, the electrode arrays are mounted to the elongated member inan axial arrangement to allow efficient ablation of tissue along thethickness of the tissue. Optionally, additional electrode arrays may bemechanically coupled to the distal end of the elongated member toprovide a longer lesion along the thickness of the tissue.

The electrode arrays may be optionally deployable from the elongatedmember. When deployed, the electrode arrays may assume variousgeometries. For example, the active electrode arrays may assume anoutwardly curved shape when deployed. The active electrode arrays mayfurther assume an everted shape. For example, both active electrodearrays can assume a proximally everted shape. Or a proximal activeelectrode array can assume a distally everted shape, and a distal activeelectrode array can assume a proximally everted shape. The returnelectrode array may assume an outwardly straight shape.

The electrode arrays may be deployed in a variety of manners. Forexample, the elongated member may comprise an inner shaft and a cannulahaving a lumen in which the inner shaft is reciprocatably disposed. Inthis case, the electrode arrays may be mounted to the inner shaft, andcan be alternately deployed from and housed within the cannula lumen.Alternatively, the cannula can be an inner cannula, in which case, theprobe assembly can further comprise an outer cannula having a lumen inwhich the inner cannula is reciprocatably disposed. Instead of beingmounted to the inner shaft, one of the two electrode arrays may bemounted to the inner cannula and can be alternately deployed from andhoused within the outer cannula lumen. This latter deployment techniqueis especially useful if the active electrode arrays are to be deployedin opposite directions.

In accordance with a third aspect of the present invention, a tissueablation system is provided. The tissue ablation system comprises amedical probe assembly, such as one of those previously described. Thetissue ablation system further comprises an ablation source (such as,e.g., a radio frequency ablation source) electrically coupled to the twoelectrode elements and the other electrode element, such that ablationenergy can be delivered between the electrode elements. The tissueablation system further comprises a controller for configuring theelectrode elements in bipolar electrode pairs in the manner previouslydescribed. The controller is configured for causing the ablation sourceto simultaneously or sequentially convey ablation energy to the bipolarelectrode pairs.

In accordance with a fourth aspect of the present inventions, a methodof treating tissue having a diseased region (e.g., a tumor) is provided.The method comprises placing two electrode elements in contact with thediseased region, and placing another electrode elements in contact withthe diseased region in an axial arrangement with the two electrodeelements, wherein the other electrode element is between the twoelectrode elements. The electrode elements may be on a single device, ordistributed among at least two separate devices. The method furthercomprises conveying ablation energy between the two electrode elementsand the other element to create two lesions within the diseased region,wherein the two lesions, in composite, form a three-dimensional lesion.The ablation energy can either be conveyed from the two electrodeelements to the other electrode element, or from the other electrodeelement to the two electrode elements. The electrode elements may bemounted on a single ablation probe or on two or more ablation probes.

Thus, it can be appreciated that the distance that the ablation energymust travel between electrode elements is half that of the spacingbetween the two electrode elements. As a result, a more efficientablation process is achieved. If the diseased region has a thickness,the two electrode elements and other electrode element can bedistributed along the thickness of the diseased region, in which case,the three-dimensional lesion can be advantageously created through thethickness of the diseased region without moving the two electrodeelements and other electrode element.

The method may optionally comprise placing an additional electrodeelement in contact with the tissue, and conveying ablation energybetween the additional electrode element and one of the two electrodeelements. In this manner, longer three-dimensional lesions may becreated and/or the distance over which the ablation energy travels maybe further reduced. In any event, the ablation energy may besimultaneously conveyed between the two electrode elements and the otherelectrode element in order to simultaneously create the two lesions, orthe ablation energy may be sequentially conveyed between the twoelectrode elements and the other electrode element in order tosequentially create the two lesions. In either case, the two lesionscompositely form the three-dimensional lesion.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of a prior art monopolar electrode arrangementbetween an electrode array and an external patch;

FIG. 2 is a plan view of a prior art bipolar electrode arrangementbetween needle electrodes on an electrode array;

FIG. 3 is a plan view of a prior art bipolar electrode arrangementbetween two needle electrode arrays;

FIG. 4 is a plan view of a tissue ablation system constructed inaccordance with one preferred embodiment of the present invention;

FIG. 5 is a perspective view of a preferred ablation probe assembly usedin the tissue treatment system of FIG. 1, wherein the probe assembly isparticularly shown in its retracted state;

FIG. 6 is a perspective view of the probe assembly of FIG. 5, whereinthe probe assembly is particularly shown in its deployed state;

FIG. 7 is a close up view of the distal end of the deployed probeassembly of FIG. 6;

FIG. 8 is a close up view of the distal end of the retracted probeassembly of FIG. 5;

FIGS. 9A-9D are cross-sectional views of one preferred method of usingthe tissue ablation system of FIG. 4 to treat tissue;

FIGS. 10A-10C are cross-sectional views of two different bipolararrangements of the probe assembly of FIGS. 5 and 6, particularlyshowing the use of distal and proximal active electrode arrays and amedial return electrode array;

FIGS. 11A-11C are cross-sectional views of two different bipolararrangements of the probe assembly of FIGS. 5 and 6, particularlyshowing the use of a medial active electrode array and distal andproximal return electrode arrays;

FIG. 12 is a perspective view of another ablation probe assembly thatcan alternatively be used in the tissue treatment system of FIG. 1,wherein the probe assembly is particularly shown in its deployed state;

FIGS. 13A-13E are cross-sectional views of two bipolar differentarrangements of the probe assembly of FIG. 12, particularly showing theuse of distal, medial, and proximal active electrode arrays and distaland proximal return electrode arrays;

FIGS. 14A-14E are cross-sectional views of two different bipolararrangements of the probe assembly of FIG. 12, particularly showing theuse of distal and proximal active electrode arrays, and distal, medial,and proximal return electrode arrays;

FIG. 15 is a perspective view of still another ablation probe assemblythat can alternatively be used in the tissue treatment system of FIG. 1,wherein the probe assembly is particularly shown in its retracted state;

FIG. 16 is a perspective view of the probe assembly of FIG. 15, whereinthe probe assembly is particularly shown in its partially deployedstate;

FIG. 17 is a perspective view of the probe assembly of FIG. 15, whereinthe probe assembly is particularly shown in its fully deployed state;

FIGS. 18A-18C are cross-sectional views of one preferred method of usingthe tissue ablation system of FIG. 4, with the alternative probeassembly of FIG. 15, to treat tissue;

FIG. 19 is a perspective view of still another ablation probe assemblythat can alternatively be used in the tissue treatment system of FIG. 1,wherein the probe assembly is particularly shown in its retracted state;

FIG. 20 is a perspective view of the probe assembly of FIG. 19, whereinthe probe assembly is particularly shown in its deployed state; and

FIG. 21 is a cross-section view of a bipolar arrangement of the probeassembly of FIG. 19 being operated to treat tissue.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 illustrates a tissue ablation system 100 constructed inaccordance with a preferred embodiment of the present invention. Thetissue ablation system 100 generally comprises a probe assembly 102configured for introduction into the body of a patient for ablativetreatment of target tissue, a radio frequency (RF) generator 104configured for supplying RF energy to the probe assembly 102 in acontrolled manner, and a cable 106 electrically connecting the probeassembly 102 to the RF generator 104.

Referring specifically now to FIGS. 5 and 6, the probe assembly 102generally comprises an elongated cannula 108 and an inner probe 110slidably disposed within the cannula 108. The cannula 108 has a proximalend 112, a distal end 114, and a central lumen 116 (shown in phantom inFIG. 5) extending through the cannula 108. As will be described infurther detail below, the cannula 108 may be rigid, semi-rigid, orflexible depending upon the designed means for introducing the cannula108 to the target tissue. The cannula 108 is composed of a suitablematerial, such as plastic, metal or the like, and has a suitable length,typically in the range from 5 cm to 30 cm, preferably from 10 cm to 20cm. If composed of an electrically conductive material, the cannula 108is preferably covered with an insulative material. The cannula 108 hasan outside diameter consistent with its intended use, typically beingfrom 1 mm to 5 mm, usually from 1.3 mm to 4 mm. The cannula 108 has aninner diameter in the range from 0.7 mm to 4 mm, preferably from 1 mm to3.5 mm.

The inner probe 110 comprises a reciprocating shaft 118 having aproximal end 120 (shown in FIG. 5) and a distal end 122 (shown in FIG.6), and three axially aligned electrode arrays 124 (shown in FIG. 6),each of which comprises a plurality of tissue penetrating needleelectrodes 126 suitably mounted to the distal end 122 of the inner probeshaft 118. The three electrode arrays 124 are configured into twobipolar electrode pairs, with the electrode array 124(2) being common tothe electrode pairs. That is, a first electrode pair is formed by theelectrode arrays 124(1) and 124(2), and a second electrode pair isformed by the electrode arrays 124(3) and 124(2). The electrode array124(2) has a polarization that is opposite to the polarization of theelectrode arrays 124(1) and 124(3). In the illustrated embodiment, theelectrode arrays 124(1) and 124(3) are configured as distal and proximalactive arrays (i.e., electrode arrays from which ablation energy isconveyed), respectively, and the electrode array 124(2) is configured asa return array (i.e., electrode array to which ablation energy isconveyed).

Like the cannula 108, the inner probe shaft 118 is composed of asuitable material, such as plastic, metal or the like. It can beappreciated that longitudinal translation of the inner probe shaft 118relative to the cannula 108 in a distal direction 132 deploys theelectrode arrays 124 from the distal end 114 of the cannula 108 (FIG.6), and longitudinal translation of the inner probe shaft 118 relativeto the cannula 108 in a proximal direction 134 retracts the electrodearrays 124 into the distal end 114 of the cannula 108 (FIG. 5). As bestseen in FIGS. 7 and 8, the cannula 108 comprises a distal opening 136 inwhich the cannula lumen 116 terminates, and circumferentially disposedports 139 that extend through the wall of the cannula 108. The needleelectrodes 126 of the distal active array 124(1) deploy out from thedistal opening 136, and the needle electrodes 126 of the return array124(2) and the proximal active array 124(3) deploy out from the ports139. Preferably, the ports 139 are somewhat elongated and extend in thedistal direction in order to facilitate deployment of the needleelectrodes 126 when the probe shaft 118 is distally displaced. Asillustrated in FIG. 8, the distal ends of the needle electrodes 126,when retracted, reside within the ports 139 in order to facilitatemovement of the needle electrodes 126 from the ports 139 duringdeployment.

Each of the individual needle electrodes 126 takes the form of a smalldiameter metal element, which can penetrate into tissue as it isadvanced from a target site within the target region. The needleelectrodes 126 are resilient and pre-shaped to assume a desiredconfiguration when advanced into tissue. When deployed from the cannula108 (FIG. 7), each of the active electrode arrays 124(1) and 124(3) isplaced in a three-dimensional configuration that defines a generallyellipsoidal or spherical volume having a periphery with a maximum radiusin the range from 0.5 to 3 cm. The needle electrodes 126 of the activearrays 124(1) and 124(3) are curved and diverge radially outwardly fromthe cannula 108 in a uniform pattern, i.e., with the spacing betweenadjacent needle electrodes 126 diverging in a substantially uniformand/or symmetric pattern. In the illustrated embodiment, the needleelectrodes 126 of the active arrays 124(1) and 124(3) also evertproximally, so that they face partially or fully in the proximaldirection 134 when fully deployed. When deployed from the cannula 108,the return electrode array 124(2) is placed in a planar configurationthat is generally orthogonal to the axis of the inner probe shaft 118.The needle electrodes 126 of the return array 124(2) are straight andextend radially outward from the cannula 108.

In exemplary embodiments, for any of the electrode arrays 124, pairs ofadjacent needle electrodes 126 can be spaced from each other in similaror identical, repeated patterns and can be symmetrically positionedabout an axis of the inner probe shaft 118. It will be appreciated thata wide variety of particular patterns can be provided to uniformly coverthe region to be treated. It should be noted that a total of six needleelectrodes 126 for each array 124 are illustrated in FIG. 4. Additionalneedle electrodes 126 can be added in the spaces between the illustratedelectrodes 126, with the maximum number of needle electrodes 126determined by the electrode width and total circumferential distanceavailable (i.e., the needle electrodes 126 could be tightly packed).

Each individual needle electrode 126 is preferably composed of a singlewire that is formed from resilient conductive metals having a suitableshape memory, such as stainless steel, nickel-titanium alloys,nickel-chromium alloys, spring steel alloys, and the like. The wires mayhave circular or non-circular cross-sections, but preferably haverectilinear cross-sections. In this manner, the needle electrodes 126are generally stiffer in the transverse direction and more flexible inthe radial direction. By increasing transverse stiffness, propercircumferential alignment of the needle electrodes 126 within thecannula 108 is enhanced. Exemplary needle electrodes will have a width(in the circumferential direction) in the range from 0.2 mm to 0.6 mm,preferably from 0.35 mm to 0.40 mm, and a thickness (in the radialdirection) in the range from 0.05 mm to 0.3 mm, preferably from 0.1 mmto 0.2 mm. The distal ends of the needle electrodes 126 may be honed orsharpened to facilitate their ability to penetrate tissue. The distalends of these needle electrodes 126 may be hardened using conventionalheat treatment or other metallurgical processes.

The probe assembly 102 further comprises a connector assembly 138, whichincludes a connector sleeve 140 mounted to the proximal end 112 of thecannula 108 and a connector member 142 slidably engaged with the sleeve140 and mounted to the proximal end 120 of the probe shaft 118. Theconnector member 142 also comprises an electrical connector 144 to whichthe probe shaft 118 is electrically coupled. The connector assembly 138can be composed of any suitable rigid material, such as, e.g., metal,plastic, or the like.

Further details regarding the general structure of needle electrodearray-type probe arrangements are disclosed in U.S. Pat. No. 6,379,353,which is hereby expressly incorporated herein by reference.

RF current is delivered to the electrode arrays 124 in a bipolarfashion. In particular, RF current will be conveyed from the activeelectrode arrays 124(1) and 124(3) to the return electrode array 124(2).Because the RF energy need only travel a distance equal to one-half thespacing between the active electrode arrays 124(1) and 124(3) (i.e.,between the distal active electrode array 124(1) and the returnelectrode array 124(2), and between the proximal active electrode array124(3) and the return electrode array 124(2)), a more efficient ablationprocess can be performed, as will be described in further detail below.

In order to oppositely polarize the return electrode array 124(2) andthe active electrode arrays 124(1) and 124(3), the active electrodearrays 124(1) and 124(3) must be electrically isolated from the returnelectrode array 124(2) through the probe assembly 102. This can beaccomplished in a variety of manners.

For example, insulated RF wires can be routed through the inner probeshaft 118 between the needle electrodes 126 of the respective arrays 124and the electrical connector 144. In this case, the inner probe shaft118 and the cannula 108 are preferably composed of an electricallynon-conductive material, so that the needle electrodes 126 of the activearrays 124(1) and 124(3) remain electrically isolated from the needleelectrodes 126 of the return array 124(3), notwithstanding that theneedle electrodes 126 of the arrays 124 are in contact with the innerprobe shaft 118 and cannula 108. Alternatively, the inner probe shaft118 and/or cannula 108 may be composed of an electrically conductivematerial, such as stainless steel, in which case, the portions of theneedle electrodes 126 that are in contact with the inner probe shaft 118and/or cannula 108 can be coated with an electrically insulativematerial. If the cannula 108 is electrically conductive, the outersurface of the cannula 108 is also preferably coated within anelectrically insulative material. Alternatively, rather than usingintermediate conductors, the proximal ends of the needle electrodes 126may be directly coupled to the connector 144, in which case, theportions of the needle electrodes 126 extending through the inner probeshaft 118 are coated with an electrically insulative material.

Alternatively, the electrically conductive shaft 118 may serve as anintermediate conductor between the active arrays 124(1) and 124(3) andthe electrical connector 144, or the return array 124(2) and theelectrical connector 144, but not both. In this case, the needleelectrodes 126 of the active arrays 124(1) and 124(3) may be inelectrical contact with the inner probe shaft 118, while the needleelectrodes 126 of the return array 124(2) may be electrically isolatedfrom the inner probe shaft 118 using an insulative coating. Or theneedle electrodes 126 of the return array 124(2) may be in electricalcontact with the inner probe shaft 118, while the needle electrodes 126of the active arrays 124(1) and 124(3) may be electrically isolated fromthe inner probe shaft 118 using an insulative coating. In some cases, aswill be described in further detail below, it may be desirable to alsoelectrically isolate the active arrays 124(1) and 124(3) from eachother. In this case, only one of the arrays 124(1) and 124(3) should bein electrical contact with the inner probe shaft 118.

Referring back to FIG. 1, the RF generator 104 is electrically connectedto the electrical connector 144 of the connector assembly 138, which aspreviously described, is directly or indirectly electrically coupled tothe electrode arrays 124. The RF generator 104 is a conventional RFpower supply that operates at a frequency in the range from 200 KHz to1.25 MHz, with a conventional sinusoidal or non-sinusoidal wave form.Such power supplies are available from many commercial suppliers, suchas Valleylab, Aspen, and Bovie. Most general purpose electrosurgicalpower supplies, however, operate at higher voltages and powers thanwould normally be necessary or suitable for vessel occlusion. Thus, suchpower supplies would usually be operated at the lower ends of theirvoltage and power capabilities. More suitable power supplies will becapable of supplying an ablation current at a relatively low voltage,typically below 150V (peak-to-peak), usually being from 50V to 100V. Thepower will usually be from 20 W to 200 W, usually having a sine waveform, although other wave forms would also be acceptable. Power suppliescapable of operating within these ranges are available from commercialvendors, such as Boston Scientific Corporation of San Jose, Calif., whomarkets these power supplies under the trademarks RF2000™ (100 W) andRF3000™ (200 W). As previously mentioned, the RF generator 104 operatesthe electrode arrays 124 in a bipolar fashion.

In the illustrated embodiment, the RF generator 104 comprises a RFablation source 146, a controller 148, and a switch 150. As will bedescribed in further detail below, the controller 148 is configured tocontrol the switch 148 in order to simultaneously or sequentiallyprovide RF energy from the ablation source 146 to the active electrodearrays 124(1) and 124(3), resulting in the desired lesion.

Having described the structure of the tissue ablation system 100, itsoperation in treating targeted tissue will now be described. Thetreatment region may be located anywhere in the body where hyperthermicexposure may be beneficial. Most commonly, the treatment region willcomprise a solid tumor within an organ of the body, such as the liver,kidney, pancreas, breast, prostrate (not accessed via. the urethra), andthe like. The volume to be treated will depend on the size of the tumoror other lesion, typically having a total volume from 1 cm³ to 150 cm³,and often from 2 cm³ to 35 cm³. The peripheral dimensions of thetreatment region may be regular, e.g., spherical or ellipsoidal, butwill more usually be irregular. The treatment region may be identifiedusing conventional imaging techniques capable of elucidating a targettissue, e.g., tumor tissue, such as ultrasonic scanning, magneticresonance imaging (MRI), computer-assisted tomography (CAT),fluoroscopy, nuclear scanning (using radiolabeled tumor-specificprobes), and the like. Preferred is the use of high resolutionultrasound of the tumor or other lesion being treated, eitherintraoperatively or externally.

Referring now to FIGS. 9A-9D, the operation of the tissue ablationsystem 100 is described in treating a treatment region TR within tissueT located beneath the skin or an organ surface S of a patient. Thetissue T prior to treatment is shown in FIG. 9A. The probe assembly 102is first introduced within the treatment region TR, so that the distalend 114 of the cannula 108 is located at the target site TS, as shown inFIG. 9B. This can be accomplished using any one of a variety oftechniques. In some cases, the probe assembly 102 may be introduced tothe target site TS percutaneously directly through the patient's skin orthrough an open surgical incision. In this case, the cannula 108 mayhave a sharpened tip, e.g., in the form of a needle, to facilitateintroduction to the treatment region TR. In such cases, it is desirablethat the cannula 108 or needle be sufficiently rigid, i.e., have asufficient column strength, so that it can be accurately advancedthrough tissue T. In other cases, the cannula 108 may be introducedusing an internal stylet that is subsequently exchanged for the innerprobe 110. In this latter case, the cannula 108 can be relativelyflexible, since the initial column strength will be provided by thestylet. More alternatively, a component or element may be provided forintroducing the cannula 108 to the target site TS. For example, aconventional sheath and sharpened obturator (stylet) assembly can beused to initially access the tissue T. The assembly can be positionedunder ultrasonic or other conventional imaging, with theobturator/stylet then removed to leave an access lumen through thesheath. The cannula 108 and inner probe 110 can then be introducedthrough the sheath lumen, so that the distal end 114 of the cannula 108advances from the sheath into the target site TS.

After the cannula 108 is properly placed, the inner probe shaft 118 isdistally advanced to deploy the electrode arrays 124 radially outwardfrom the distal end 114 of the cannula 108, as shown in FIG. 9C.Preferably, the electrode arrays 124 are axially disposed along theentire thickness of the treatment region TR. The RF generator 104 isthen connected to the connector assembly 138 via the electricalconnector 144 and then operated to create a three-dimensional lesion Lwithin the treatment region TR, as illustrated in FIG. 9D.

In particular, the RF generator 104 is configured to simultaneouslyconvey RF energy from the active electrode arrays 124(1) and 124(3) tothe return electrode array 124(2). This can be accomplished by thecontroller 148, which operates the switch 150 to couple the ablationsource 146 to the active arrays 124(1) and 124(3), while the returnarray 124(2) is grounded. Thus, RF energy is conveyed from the distalactive array 124(1), through the tissue, to the return array 124(2) tocreate a first lesion portion L1, and from the proximal active array124(3), through the tissue, to the return array 124(2) to create asecond lesion portion L2 (FIG. 1A). The composite of the lesion portionsL1 and L2 forms the lesion L.

Alternatively, the RF generator 104 may be configured to sequentiallyconvey RF energy from the active electrode arrays 124(1) and 124(3) tothe return electrode array 124(2). In particular, with the return array124(2) grounded, the controller 148 operates the switch 150 to firstcouple the ablation source 146 to the distal active array 124(1) anddecouple the ablation source 146 from the proximal active array 124(3),while conveying RF energy from the ablation source 146. In this manner,RF energy is conveyed to the distal active array 124(1), which in turn,is transmitted through the tissue to the return array 124(2) to create afirst lesion portion L1, as illustrated in FIG. 10B. The controller 148may then operate the switch 150 to decouple the ablation source 146 fromthe distal active array 124(1) and couple the ablation source 146 to theproximal active array 124(3), while continuing to convey RF energy fromthe ablation source 146. In this manner, RF energy is then conveyed tothe proximal active array 124(3), which in turn, is transmitted throughthe tissue to the return array 124(2) to create a second lesion portionL2, as illustrated in FIG. 10C.

Thus, it can be appreciated that the treatment system 100 may createmultiple bipolar ablation zones (in this case, two) through thethickness of the treatment region TR. Because there are two ablationzones, the ablation process is made more efficient, since the tissuedistance between any pair of electrodes is reduced by one-half. This, incombination, with the axial arrangement of the electrode arrays 124 mayobviate the need to perform stacked ablations through the thickness ofthe treatment region TR. In addition, because the electrode arrays 124radially extend outward, a three-dimensional lesion is created, incontrast to a linear lesion that is typically created using electrodeelements that do not extend radially outward, such as ring electrodes.As a result, only one ablation procedure may be needed to ablate theentire treatment region TR (i.e., without repositioning the ablationprobe between ablations), or at the least, the number of ablationprocedures required to do so will be minimized.

It should be noted that although the electrode arrays 124 werepreviously described as being configured in a bipolar arrangement byconveying RF current from the electrode arrays 124(1) and 124(3) to theelectrode array 124(2), the electrode arrays 124 may be configured in abipolar arrangement by conveying RF current from the electrode array124(2) to the electrode arrays 124(1) and (3). In this case, theelectrode arrays 124(1) and 124(3) will serve as distal and proximalreturn arrays, and the electrode array 124(2) will serve as an activearray.

For example, the RF generator 104 may be configured to simultaneouslyconvey RF energy from the active electrode array 124(2) to the returnelectrode arrays 124(1) and 124(3). This can be accomplished by thecontroller 148, which can operate the switch 150 to couple the ablationsource 146 to the active array 124(2), while the return arrays 124(1)and 124(2) are grounded. Thus, RF energy is conveyed from the activearray 124(2), through the tissue, to the distal return array 124(1) tocreate a first lesion portion L1, and from the active array 124(2),through the tissue, to the proximal return array 124(3) to create asecond lesion portion L2 (FIG. 11A). The composite of the lesionportions L1 and L2 forms the lesion L.

Alternatively, the RF generator 104 may be configured to sequentiallyconvey RF energy from the active electrode array 124(2) to the returnelectrode arrays 124(1) and 124(3). In particular, with the ablationsource 146 coupled to the active array 124(2), the controller 148 mayoperate the switch 150 to ground the distal return array 124(1) andunground the proximal return array 124(3), while conveying RF energyfrom the ablation source 146. In this manner, RF energy is conveyed tothe active array 124(2), which in turn, is transmitted through thetissue to the distal return array 124(1) to create a first lesionportion L1, as illustrated in FIG. 11B. The controller may then ungroundthe distal return array 124(1) and ground the proximal return array124(3), while continuing to convey RF energy from the ablation source146. In this manner, RF energy continues to be conveyed to the activearray 124(2), which in turn, is transmitted through the tissue to theproximal return array 124(3) to create a second lesion portion L2, asillustrated in FIG. 11C.

Regardless of which manner the electrode arrays 124 are placed in abipolar arrangement, ablation probe assemblies constructed in accordancewith the present invention can also generate more than two ablationzones. For example, with reference to FIG. 12, a probe assembly 202 thatgenerates four ablation zones will now be described. The probe assembly202 is similar to the previously described probe assembly 202, with theexception that it comprises an inner probe 210 that carries five axiallyarranged electrode arrays 224(1)-224(5) that are configured to form fourbipolar electrode pairs. The electrode arrays 224(2) and 224(4) have apolarization that is opposite to the polarization of the electrodearrays 224(1), 224(3), and 224(5). In the illustrated embodiment, theelectrode arrays 224(1), 224(3), and 224(5) are configured as distal,medial, and proximal active arrays, respectively, and the electrodearrays 224(2) and 224(4) are configured as distal and proximal returnarrays, respectively. Thus, it can be appreciated that the electrodearray 224(2) is common to a first bipolar electrode pair formed byelectrode arrays 224(1) and 224(2) and a second bipolar electrode pairformed by electrode arrays 224(3) and 224(2). The electrode array 224(3)is common to the second bipolar electrode pair and a third bipolarelectrode pair formed by electrode arrays 224(4) and 224(3). Theelectrode array 224(4) is common to the third bipolar electrode pair anda fourth bipolar electrode pair formed by electrode arrays 224(5) and224(4).

As illustrated in FIG. 12, longitudinal translation of the inner probeshaft (not shown) relative to the cannula 108 in the distal direction132 deploys the electrode arrays 224 from the distal end 114 of thecannula 108. The needle electrodes 126 of the distal active electrodearray 224(1) deploy out from the distal opening (not shown) within theinner probe shaft 118, and the needle electrodes 126 of the remainingelectrode arrays 224(2)-224(5) deploy out from distal openings (notshown) formed through the wall of the cannula 108.

As with the previously described electrode arrays 124, RF current isdelivered to the electrode arrays 224 in a bipolar fashion. Inparticular, RF current will be conveyed from the active electrode arrays224(1), 224(3), and 224(5) to the return electrode array 224(2) and224(4). Because the RF energy need only travel a distance equal toone-quarter the spacing between the active electrode arrays 124(1) and124(5) (i.e., between the distal active electrode array 224(1) and thedistal return electrode array 224(2), between the medial activeelectrode array 224(3) and the distal return electrode array 224(2),between the medial active electrode array 224(3) and the proximal returnelectrode array 224(4), and between the proximal active electrode array224(5) and the proximal return electrode array 224(4)), a more efficientablation process can be performed.

In order to oppositely polarize the active electrode arrays 224(1),224(3), and 224(5) and the return electrode arrays 224(2) and 224(4),the active electrode arrays 224(1), 224(3), and 224(5) must beelectrically isolated from the return electrode arrays 224(2) and224(4). This can be accomplished in the same manner that the electrodearrays 124(1) and 124(3) and the electrode array 124(2) are electricallyisolated, as previously described above.

Using the probe assembly 202, instead of the probe assembly 102, thesystem 100 can be operated in the same manner as previously described,with the exception that three active electrode arrays and two returnelectrode arrays will be configured in a bipolar arrangement. Ingeneral, long lesions can be created by the probe assembly 202. Inparticular, the RF generator 104 is configured to simultaneously conveyRF energy from the active electrode arrays 224(1), 224(3), and 224(5) tothe return electrode arrays 224(2) and 224(4). This can be accomplishedby the controller 148, which can operate the switch 150 to couple theablation source 146 to the active arrays 124(1), 124(3), and 124(5),while the return arrays 124(2) and 124(4) are grounded. Thus, RF energyis conveyed from the distal active array 224(1), through the tissue, tothe distal return array 224(2) to create a first lesion portion L1, fromthe medial active array 224(3), through the tissue, to the distal returnarray 224(2) to create a second lesion portion L2, from the medialactive array 224(3), through the tissue, to the proximal return array224(4) to create a third lesion portion L3, and from the proximal activearray 224(5), through the tissue, to the proximal return array 224(4) tocreate a fourth lesion portion L4 (FIG. 13A). The composite of thelesion portions L1-L4 forms the lesion L.

Alternatively, the RF generator 104 may be configured to sequentiallyconvey RF energy from the active electrode arrays 224(1), 224(3), and224(5) to the return electrode arrays 224(2) and 224(4). In particular,with the ablation source 146 decoupled from the medial and proximalactive arrays 224(3) and 224(5), and the proximal return array 224(4)grounded, the controller 148 may first operate the switch 150 to firstcouple the ablation source 150 to the distal active array 224(1), whileconveying RF energy from the ablation source 150. In this manner, RFenergy is conveyed to the distal active array 224(1), which in turn, istransmitted through the tissue to the distal return array 224(2) tocreate a first lesion portion L1, as illustrated in FIG. 13B.

The controller 148 may then operate the switch 150 to decouple theablation source 146 from the distal active array 224(1) and couple theablation source 146 to the medial active array 224(3), while continuingto convey RF energy from the ablation source 146. In this manner, RFenergy is then conveyed to the medial active array 124(3), which inturn, is transmitted through the tissue to the distal return array124(2) to create a second lesion portion L2, as illustrated in FIG. 13C.The controller 148 may then unground the distal return array 224(2) andground the proximal return array 224(4), while continuing to convey RFenergy from the ablation source 146. In this manner, RF energy continuesto be conveyed to the medial active array 224(3), which in turn, istransmitted through the tissue to the proximal return array 224(4) tocreate a third lesion portion L3, as illustrated in FIG. 13D. Thecontroller 148 may then decouple the ablation source 146 from the medialactive array 224(3) and couple the ablation source 146 to the proximalactive array 224(5), while continuing to convey RF energy from theablation source 146. In this manner, RF energy is then conveyed to theproximal active array 224(5), which in turn, is transmitted through thetissue to the proximal return array 224(4) to create a fourth lesionportion L4, as illustrated in FIG. 13E.

As previously described with respect to the electrode arrays 124, theelectrode arrays 224 may be configured in another bipolar arrangement byconveying RF current from the electrode arrays 224(2) and 224(4) to theelectrode arrays 224(1), 224(3), and 224(5). In this case, the electrodearrays 224(1), 224(3), and 224(5) will serve as distal, medial, andproximal return arrays, and the electrode arrays 224(2) and 224(4) willserve as distal and proximal active arrays.

For example, the RF generator 104 may be configured to simultaneouslyconvey RF energy from the active electrode arrays 224(2) and 224(4) tothe return electrode arrays 224(1), 224(3), and 224(5). This can beaccomplished by the controller 148, which can operate the switch 150 tocouple the ablation source 146 to the active arrays 224(2) and 224(4),while the return arrays 224(1), 224(3), and 224(5) are grounded. Thus,RF energy is conveyed from the distal active array 224(2), through thetissue, to the distal return array 224(1) to create a first lesionportion L1, from the distal active array 224(2), through the tissue, tothe medial return array 224(3) to create a second lesion portion L2,from the proximal active array 224(4), through the tissue, to the medialreturn array 224(3) to create a third lesion portion L3, and from theproximal active array 224(4), through the tissue, to the proximal returnarray 224(5) to create a fourth lesion portion L4 (FIG. 14A). Thecomposite of the lesion portions L1-L4 forms the lesion L.

Alternatively, the RF generator 104 may be configured to sequentiallyconvey RF energy from the active electrode arrays 224(2) and 224(4) tothe return electrode arrays 224(1), 224(3), and 224(5). In particular,with the ablation source 146 decoupled from the proximal active array224(4), and the proximal and medial return arrays 224(2) and 224(4)grounded, the controller 148 may operate the switch 150 to first couplethe ablation source 150 to the distal active array 224(2), whileconveying RF energy from the ablation source 150. In this manner, RFenergy is conveyed to the distal active array 224(2), which in turn, istransmitted through the tissue to the distal return array 224(1) tocreate a first lesion portion L1, as illustrated in FIG. 14B. Thecontroller 148 may then unground the distal return array 224(1) andground the medial return array 224(3), while continuing to convey RFenergy from the ablation source 146. In this manner, RF energy continuesto be conveyed to the distal active array 224(2), which in turn, istransmitted through the tissue to the medial return array 124(3) tocreate a second lesion portion L2, as illustrated in FIG. 14C.

The controller may then decouple the ablation source 146 from the distalactive array 224(2) and couple the ablation source 146 to the proximalactive array 224(4), while continuing to convey RF energy from theablation source 146. In this manner, RF energy is then conveyed to theproximal active array 224(4), which in turn, is transmitted through thetissue to the medial return array 224(3) to create a third lesionportion L3, as illustrated in FIG. 14D. The controller may then ungroundthe medial return array 224(3) and ground the proximal return array224(5), while continuing to convey RF energy from the ablation source146. In this manner, RF energy continues to be conveyed from theproximal active array 224(4), which in turn, is transmitted through thetissue to the proximal return array 224(5) to create a fourth lesionportion L4, as illustrated in FIG. 14E.

Referring now to FIGS. 15-17, another probe assembly 302 that can beused in the treatment system 100 will now be described. The probeassembly 302 is similar to the previously described probe assembly 102,with the exception that the probe assembly 302 deploys the activeelectrode arrays in opposite directions. In particular, the probeassembly 302 generally comprises an outer cannula 307, an inner cannula308 slidably disposed within the cannula 307, and an inner probe 310slidably disposed within the inner cannula 308. The outer cannula 307has a proximal end 311, a distal end 313, and a central lumen 315 (shownin phantom in FIG. 15) extending through the outer cannula 307. Theinner cannula 308 has a proximal end 312, a distal end 314, and acentral lumen 316 (shown in phantom in FIGS. 15 and 16) extendingthrough the cannula 308. The outer cannula 307 and inner cannula 308 maybe composed of the same material and have the similar dimensions as thepreviously described cannula 108, with the caveat that the outer cannula307 is somewhat shorter than the inner cannula 308.

The inner probe 310 comprises a reciprocating shaft 318 having aproximal end 320 and a distal end 322, and two axially aligned electrodearrays 324(1) and 324(2), each of which comprises a plurality of tissuepenetrating needle electrodes 126 suitably mounted to the distal end 322of the inner probe shaft 318. An additional electrode array 324(3) ismounted to the distal end 314 of the inner cannula 308. The threeelectrode arrays 324 are configured into two bipolar electrode pairs,with the electrode array 324(2) being common to the electrode pairs.That is, a first electrode pair is formed by the electrode arrays 324(1)and 324(2), and a second electrode pair formed by the electrode arrays324(3) and 324(2). The electrode array 324(2) has a polarization that isopposite to the polarization of the electrode arrays 324(1) and 324(3).In the illustrated embodiment, the electrode arrays 324(1) and 324(3)are configured as distal and proximal active arrays, and the electrodearray 324(2) is configured as a return array.

It can be appreciated that longitudinal translation of the inner probeshaft 318 relative to the inner cannula 308 in the distal direction 132deploys the electrode arrays 324(1) and 324(2) from the distal end 314of the inner cannula 308 (FIG. 17), and longitudinal translation of theinner probe shaft 318 relative to the inner cannula 308 in the proximaldirection 134 retracts the electrode arrays 324(1) and 324(2) into thedistal end 314 of the inner cannula 308 (FIG. 15). The inner cannula 308comprises a distal opening (not shown) in which the cannula lumen 316terminates, and circumferentially disposed ports (not shown) that extendthrough the wall of the inner cannula 308. The needle electrodes 126 ofthe distal active array 324(1) deploy out from the distal opening, andthe needle electrodes 126 of the return array 324(2) deploy out from thedistal ports.

Longitudinal translation of the inner cannula 308 relative to the outercannula 307 in the proximal direction 132 deploys the proximal activeelectrode array 324(3) from the distal end 314 of the outer cannula 307(FIG. 16), and longitudinal translation of the inner cannula 308relative to the outer cannula 307 in the distal direction 134 retractsthe proximal active electrode array 324(3) into the distal end 313 ofthe outer cannula 307. (FIG. 15). The outer cannula 307 comprisescircumferentially disposed ports (not shown) that extend through thewall of the outer cannula 307. The needle electrodes 126 of the proximalactive array 324(3) deploy out from the distal ports.

As can be seen in FIG. 17, the geometry of the deployed electrode arrays324(1), 324(2), and 324(3) are the same as the geometry of the deployedelectrode arrays 124(1), 124(2), and 124(3), respectively, with theexception that the needle electrodes 126 of the proximal active array324(3) evert distally, so that they face partially or fully in thedistal direction 132 when fully deployed. The probe assembly 302 furthercomprises a connector assembly 338, which is similar to the previouslydescribed connector assembly 138, with the exception that it includes anadditional connector sleeve 340 mounted to the proximal end 311 of theouter cannula 307.

In order to provide a more efficient ablation process, RF current can bedelivered to the electrode arrays 324 in a bipolar fashion in the samemanner as RF current is delivered to the respective electrode arrays 124described above. The only difference is that, if desired, RF current maybe delivered to the electrode array 324(3) via the electricallyconductive inner cannula 308, rather than the inner probe shaft 318.

Referring now to FIGS. 18A-18D, the operation of the probe assembly 302in treating a treatment region TR within tissue T located beneath theskin or an organ surface S of a patient. The operation of the probeassembly 302 is similar to that of the probe assembly 102, with theexception that the deployment process differs. In particular, the probeassembly 302, while fully retracted, is first introduced within thetreatment region TR, so that the distal end 316 of the inner cannula 308is located at the target site TS, as shown in FIG. 18A. This can beaccomplished in the same manner as the previously described probeassembly 302.

After the probe assembly 302 is properly placed, the connector sleeve140 of the connector assembly 338 is pulled proximally relative to theconnector sleeve 138, thereby proximally displacing the inner cannula308 relative to the outer cannula 307. As a result, the proximal activeelectrode array 324(3) is deployed radially outward from the distalopenings within the outer cannula 307, as shown in FIG. 18B. Notably,the distal end 316 of the inner cannula 308 is proximally displacedwithin the treatment region TR. Thus, the target site TS will generallybe located distal to the treatment region TR, so that when the distalend 316 of the inner cannula 308 will reside within the treatment regionTR when the proximal active electrode array 324(3) is deployed.

Next, the connector member 142 is pushed distally relative to theconnector sleeve 140, thereby distally displacing the inner probe shaft318 relative to the inner cannula 308. As a result, the distal activeelectrode array 324(1) is deployed radially outward from the distalopening of the inner cannula 308, and the return electrode array 324(2)is deployed radially outward from the distal openings within the innercannula 308, as shown in FIG. 18C. The RF generator 104 is thenconnected to the connector assembly 138 via the electrical connector 144and then operated to create a three-dimensional lesion L within thetreatment region TR similar to that illustrated in FIG. 9D. Thedifference is that there will generally be more symmetry in the lesioncreated by the probe assembly 302, since the oppositely everted activeelectrode arrays 324(1) and 324(3) will be geometrically symmetricalabout the planar return electrode array 324(2).

In the preferred embodiment, RF current is simultaneously conveyed fromthe distal and proximal active electrode arrays 324(1) and 324(3) to thereturn electrode array 324(2). This can be accomplished in the samemanner previously described above with respect to FIG. 10A.Alternatively, RF current can be sequentially conveyed from the distaland proximal active electrode arrays 324(1) and 324(3) to the returnelectrode array 324(2). This can be accomplished in the same mannerpreviously described above with respect to FIGS. 10B and 10C. Or theelectrode arrays 324(1) and 324(3) can be operated as return arrays, andthe electrode array 324(2) can be operated as an active array, in whichcase, RF current can be simultaneously or sequentially delivered fromthe active electrode array 324(2) to the return electrode arrays 324(1)and 324(3). This can be accomplished in the same manner previouslydescribed above with respect to FIG. 11A or FIGS. 1B and 11C,respectively.

Referring now to FIGS. 19 and 20, another probe assembly 402 that canalternatively be used in the treatment system 100 will now be described.The probe assembly 402 is similar to the previously described probeassembly 102, with the exception that the active electrode elements ofthe probe assembly 402 are ring electrodes, rather than electrodearrays. In particular, the probe assembly 402 generally comprises acannula 408 and an inner probe 410 slidably disposed within the cannula408. The cannula 408 has a proximal end 412, a distal end 414, and acentral lumen 416 (shown in phantom in FIG. 19) extending through thecannula 408.

The inner probe 410 comprises a reciprocating shaft 418 having aproximal end 420 and a distal end 422, and an electrode array 424(2),which comprises a plurality of tissue penetrating needle electrodes 126suitably mounted to the distal end 422 of the inner probe shaft 418. Thecannula 408 comprises two axially aligned ring electrodes 424(1) and424(3) disposed along the shaft of the cannula 408. The ring electrodes424(1) can be formed on the cannula 408 in any one of a variety of ways.In the illustrated embodiment, the cannula 408, itself, is electricallyconductive, so that annular portions of the cannula 408 can form thering electrodes 424(1) and 424(3). The lengthwise portions of thecannula 408 between the ring electrodes 424(1) and 424(3) are coveredwithin an insulative material in order to concentrate the ablationenergy at the ring electrodes 424(1) and 424(3). Alternatively, the ringelectrodes 424(1) and 424(3) can be discrete electrically conductiverings that are circumferentially mounted around the cannula 408. In thiscase, electrically conductors (not shown) can be mounted to the ringelectrodes 424(1) and 424(3) routed back through the cannula lumen 416to the proximal end 412. The cannula 408 can either be composed of, orcovered with, an insulative material, so that the ablation energy can befocused at the ring electrodes 424(1) and 424(3). Optionally, a portionof the needle electrodes 126 of the return array 424(2) can be coatedwith an insulative material (not shown), with the distal ends of theneedle electrodes 126 exposed. In this manner, the resulting lesion thatis generated by the probe assembly 102 can be shaped. For example, theablation energy can be focused at the distal tips of the needleelectrodes 126 in order to provide greater lesion coverage.

The three electrode arrays 424 are configured into two bipolar electrodepairs, with the electrode array 424(2) being common to the electrodepairs. That is, a first electrode pair is formed by the electrode arrays424(1) and 424(2), and a second electrode pair is formed by theelectrode arrays 424(3) and 424(2). The electrode array 424(2) has apolarization that is opposite to the polarization of the ring electrodes424(1) and 424(3). In the illustrated embodiment, the ring electrodes424(1) and 424(3) are configured as distal and proximal active elements,and the electrode array 424(2) is configured as a return array.Alternatively, the ring electrodes 424(1) and 424(3) can be configuredas distal and proximal return elements, and the electrode array 424(2)configured as an active array.

It can be appreciated that longitudinal translation of the inner probeshaft 418 relative to the inner cannula 408 in the distal direction 132deploys the electrode array 424(2) from the distal end 414 of the innercannula 408 (FIG. 20), and longitudinal translation of the inner probeshaft 318 relative to the inner cannula 308 in the proximal direction134 retracts the electrode array 424(2) into the distal end 414 of thecannula 408 (FIG. 19). The cannula 408 comprises circumferentiallydisposed ports 139 that extend through the wall of the cannula 408. Theneedle electrodes 126 of the return array 424(2) deploy out from thedistal ports 139. As can be seen in FIG. 20, the geometry of thedeployed electrode arrays 424(2) is the same as the geometry of thedeployed electrode arrays 124(2).

In order to provide a more efficient ablation process, RF current can bedelivered to the electrode arrays 424 in a bipolar fashion in the samemanner as RF current is delivered to the respective electrode arrays 124described above. Operation of the probe assembly 402 is similar to theoperation of the probe assembly 102 described with respect to FIGS.9A-9D, with the exception that a diamond shaped lesion L is generatedwithin the treatment region TR, as illustrated in FIG. 21.

It should be noted that although single ablation probes have beenpreviously described as being used to perform tissue ablation, multipleprobes can also be used. For example, first and second electrode arraysmay be mounted on first probe, and a third electrode array mounted on asecond probe. Prior to performing the actual tissue ablation, the probescan be introduced into the tissue, such that the third electrode arrayis distal to and axially aligned with the first and second electrodearrays. Thus, first and second electrode arrays on the first probe maybe characterized as proximal and medial electrode arrays, and the thirdelectrode array on the second probe may be characterized as a distalelectrode array. Alternatively, the probes can be introduced into thetissue, such that the third electrode array is proximal to and axiallyaligned with the first and second electrode arrays. Thus, first andsecond electrode arrays on the first probe may be characterized asmedial and distal electrode arrays, and the third electrode array on thesecond probe may be characterized as a proximal electrode array. Evenmore alternatively, the probes can be introduced into the tissue, suchthat the third electrode array is between and axially aligned with thefirst and second electrode arrays. In this case, the first and secondelectrode arrays on the first probe may be characterized as proximal anddistal electrode arrays, and the third electrode array on the secondprobe may be characterized as a medial electrode array. In each of theabove cases, the electrode arrays should be arranged, such that they areaxially aligned with each other, and such that the proximal and distalelectrode arrays are oppositely polarized from the medial electrodearray. The importance is that the electrode arrays be axially arranged,and that the arrangement allows ablation energy to be delivered betweenthe medial electrode array and the respective proximal and distalelectrode arrays.

Although all of the ablation processes described above use a stabilizedelectrode array arrangement throughout the treatment process, therebysimplifying and reducing the procedure time, the electrode arrayarrangement may be made more dynamic to provide for improved lesions.For example, if two ablation probes are used, a medial electrode arraylocated on a second probe can be moved closer to the distal electrodearray on the first probe when ablating therebetween, and then can bemoved closer to the proximal electrode array on the first probe whenablating therebetween. As a result, the distance between the pertinentelectrode arrays at any given time can be reduced, thereby maximizingthe efficiency of the ablation process. The same result can be achievedusing a single ablation probe by making the medial array movable alongthe axis of the probe, so that it can be distally moved to be placedcloser to the distal electrode array when ablating therebetween, andproximal moved to be placed closer to the proximal electrode array whenablating therebetween. Thus, it can be appreciated that the use ofdynamically movable electrode arrays may add more complexity to theprocess, but may provide or a more efficient and effective lesion.

It should also be noted that although the characterization of any givenelectrode array has been previously described as being either as anactive array or a return array, a given electrode array may beconfigured such that it can be dynamically selected to be either anactive array or a return array. For example, in a three-electrode arrayarrangement, the distal electrode array can be configured as an activeelectrode array, and the medial electrode array can be configured as areturn electrode array to provide a first ablation region therebetween.The medial electrode array can then be configured as an active electrodearray and the proximal electrode array can be configured as a returnelectrode array to provide a second ablation region therebetween.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. A medical probe assembly for ablating tissue, comprising: anelongated member having a distal end; two electrode elementsmechanically coupled to the distal end of the elongated member; andanother electrode element mechanically coupled to the distal end of theelongated member between the respective two electrode elements, the twoelectrode elements and other electrode element being configurable as twobipolar electrode pairs, wherein the other electrode element is commonto the bipolar electrode pairs; wherein at least one of the twoelectrode elements and other electrode element is an array comprising aplurality of electrodes radially extendable from the elongated member.2. The medical probe assembly of claim 1, wherein the elongated memberis rigid.
 3. The medical probe assembly of claim 1, wherein each of thetwo electrode elements is configurable only as an active element, andthe other electrode element is configurable only as a return element. 4.The medical probe assembly of claim 1, wherein each of the two electrodeelements is configurable only as a return element, and the otherelectrode element is configurable only as an active element.
 5. Themedical probe assembly of claim 1, wherein each of the electrodeelements comprises a plurality of electrodes radially extendable fromthe elongated member.
 6. The medical probe assembly of claim 1, whereinat least one of the two electrode elements and other electrode elementis a ring electrode.
 7. The medical probe assembly of claim 1, whereinthe two electrode elements and other electrode element are mounted tothe distal end of the elongated member in an axial arrangement.
 8. Themedical probe assembly of claim 1, further comprising an additionalelectrode element mechanically coupled to the distal end of theelongated member, wherein the two electrode elements, other electrodeelement, and additional electrode element are configurable as threebipolar electrode pairs.
 9. The medical probe assembly of claim 1,wherein the plurality of electrodes are configured to be radiallydeployed from the elongated member.
 10. A medical probe assembly forablating tissue, comprising: an elongated member having a distal end;two electrode arrays mechanically coupled to the distal end of theelongated member, each of the two electrode arrays comprising aplurality of needle electrodes; and another electrode array mechanicallycoupled to the distal end of the elongated member between the respectivetwo electrode arrays, the other electrode array comprising a pluralityof needle electrodes, the two electrode arrays and other electrode arraybeing configurable as two bipolar electrode pairs, wherein the otherelectrode array is common to the bipolar electrode pairs.
 11. Themedical probe assembly of claim 10, wherein the elongated member isrigid.
 12. The medical probe assembly of claim 10, wherein each of thetwo electrode arrays is configurable only as an active array, and theother electrode array is configurable only as a return array.
 13. Themedical probe assembly of claim 10, wherein each of the two electrodearrays is configurable only as a return array, and the other electrodearray is configurable only as an active array.
 14. The medical probeassembly of claim 10, wherein the two electrode arrays and otherelectrodes array are deployable from the elongated member.
 15. Themedical probe assembly of claim 14, wherein the needle electrodes of thetwo electrode arrays assume an outwardly curved shape when deployed. 16.The medical probe assembly of claim 14, wherein the needle electrodes ofthe two electrode arrays assume an everted shape when deployed.
 17. Themedical probe assembly of claim 16, wherein the needle electrodes ofeach of the two electrode arrays assume a proximally everted shape whendeployed.
 18. The medical probe assembly of claim 16, wherein the twoelectrode arrays comprises a proximal electrode array and a distalelectrode array, the electrodes of the proximal electrode array assume adistally everted shape when deployed, and the electrodes of the distalelectrode array assume a proximally everted shape when deployed.
 19. Themedical probe assembly of claim 14, wherein the needle electrodes of theother electrode array assume an outwardly straight shape when deployed.20. The medical probe assembly of claim 14, wherein the elongated membercomprises an inner shaft and a cannula having a lumen in which the innershaft is reciprocatably disposed, the other electrode array and at leastone of the two electrode arrays is mounted to the inner shaft, and theother electrode array and at least one of the two electrode arrays canbe alternately deployed from and housed within the cannula lumen. 21.The medical probe assembly of claim 20, wherein the other of the twoelectrode arrays is mounted to the inner shaft and can be alternatelydeployed from and housed within the cannula lumen.
 22. The medical probeassembly of claim 20, wherein the cannula is an inner cannula, themedical probe assembly further comprising an outer cannula having alumen in which the inner cannula is reciprocatably disposed, wherein theother of the two electrode arrays is mounted to the inner cannula andcan be alternately deployed from and housed within the outer cannulalumen.
 23. The medical probe assembly of claim 10, wherein the twoelectrode arrays and other electrode array are mechanically coupled tothe distal end of the elongated member in an axial arrangement.
 24. Themedical probe assembly of claim 10, further comprising an additionalelectrode array mechanically coupled to the distal end of the elongatedmember, wherein the two electrode arrays and other electrode array areconfigurable as three bipolar electrode pairs.
 25. A tissue ablationsystem, comprising: a medical probe assembly comprising an elongatedmember, two electrode elements mechanically coupled to a distal end ofthe elongated member, and another electrode element mechanically coupledto the distal end of the elongated member between the respective twoelectrode elements, and wherein at least one of the two electrodeelements and other electrode element is an array comprising a pluralityof electrodes radially extendable from the elongated member; acontroller for configuring the two electrode elements and otherelectrode element as two bipolar electrode pairs, wherein the otherelectrode element is common to the bipolar electrode pairs; and anablation source electrically coupled to the two electrode elements andthe other electrode element.
 26. The system of claim 25, wherein theelongated member is rigid.
 27. The system of claim 25, wherein thecontroller can configure each of the two electrode elements as an activeelement, and the other electrode element as a return element.
 28. Thesystem of claim 25, wherein the controller can configure each of the twoelectrode elements as a return element, and the other electrode elementas an active element.
 29. The system of claim 25, wherein the electrodesof the at least one electrode array are needle electrodes.
 30. Thesystem of claim 25, wherein each of the two electrode element and otherelectrode element comprises a plurality of electrodes radiallyextendable from the elongated member.
 31. The system of claim 25,wherein at least one of the two electrode elements and other electrodeelement is a ring electrode.
 32. The system of claim 25, wherein the twoelectrode elements and other electrode element are mounted to the distalend of the elongated member in an axial arrangement.
 33. The system ofclaim 25, wherein the medical probe assembly further comprises anadditional electrode element mechanically coupled to the distal end ofthe elongated member, wherein the controller can configure the twoelectrode elements, other electrode element, and additional electrodeelement as three bipolar electrode pairs.
 34. The system of claim 25,wherein the ablation source is a radio frequency ablation source. 35.The system of claim 25, wherein the controller is configured for causingthe ablation source to simultaneously convey ablation energy to thebipolar electrode pairs.
 36. The system of claim 25, wherein thecontroller is configured for causing the ablation source to sequentiallyconvey ablation energy to the bipolar electrode pairs.
 37. A method oftreating tissue having a diseased region, comprising: placing twoelectrode elements in contact with the diseased region; placing anotherelectrode element in contact with the diseased region in an axialarrangement with the two electrode elements, the other electrode elementbeing between the two electrode elements; and conveying ablation energybetween the two electrode elements and the other element to create twoablation regions within the diseased region, wherein the two ablationregions, in composite, form a three-dimensional lesion.
 38. The methodof claim 37, wherein the ablation energy is conveyed from the twoelectrode elements to the other electrode element.
 39. The method ofclaim 37, wherein the ablation energy is conveyed from the other elementto the two electrode elements.
 40. The method of claim 37, furthercomprising: placing an additional electrode element in contact with thetissue in the axial arrangement; and conveying ablation energy betweenthe additional electrode element and one of the two electrode element tocreate an additional ablation region within the diseased region, whereinthe two ablation regions and the additional ablation region, incomposite, create the three-dimensional lesion.
 41. The method of claim37, wherein the ablation energy is radio frequency energy.
 42. Themethod of claim 37, wherein the ablation energy is simultaneouslyconveyed between the two electrode elements and the other electrodeelement.
 43. The method of claim 37, wherein the ablation energy issequentially conveyed between the two electrode elements and the otherelectrode element.
 44. The method of claim 37, wherein the diseasedregion is a tumor.
 45. The method of claim 37, wherein the diseasedregion has a thickness, the two electrode elements and the otherelectrode element are distributed along the thickness of the diseasedregion, and the lesion is created through the thickness of the diseasedregion without moving the two electrode elements and the other electrodeelement.
 46. The method of claim 37, wherein the two electrode elementsand other electrode element are mounted on a single medical ablationprobe.
 47. The method of claim 37, wherein the two electrode elementsand other electrode element are mounted on two medical ablation probes.